Hard beads in steel to enhance strength

ABSTRACT

Hard beads can be formed in a single piece of sheet steel to enhance its strength before or after stamping. The hard beads are formed by melting and re-solidifying it in small discrete volumes. The melting can be performed by applying heat from a heat source; for example, a laser beam, an electron beam, a high temperature flame etc. The re-solidified volume of steel is the hard bead which is stronger than the remaining base steel. Preferably, the hard bead can be formed to have an elongated shape; and the tensile strength of the single piece of sheet steel is enhanced in the direction the bead is elongated. Hard beads thus formed can be arranged in a suitable pattern to meet a strength requirement of a part.

BACKGROUND OF THE INVENTION

The present invention relates generally to strength enhancement of pre- and post-fabricated steel parts and specifically, this invention discloses strength enhancement of pre- and post-fabricated steel parts by forming hard beads therein.

Application of sheet steel is found in most areas of modern technology ranging from electronics to automotive, and it is worth mentioning that the steel is a significant component of the weight and cost of the part. Recently, weight and cost reduction of a part has been a major challenge, and since steel plays a major role in determining the cost and weight of a part, it is steel that has been the focus of many endeavors. In the conventional art, a higher strength requirement of steel is met by using thicker single sheets or multiple sheets lapped together resulting in a heavier part in each case. In another example of the conventional art where weight limit is a critical factor in design consideration, high strength steel is used. However, the high strength steel costs are significantly more which results in costly pre- and -post processes, and thus increases the part cost. Further in the conventional art, heat treatment application is employed to increase the strength of the sheet steel. However, the heat treatment applications may have limitations as to what degree the strength can be enhanced, and if the treatment can be applied after stamping. Also in the conventional art, laser welded blanks having two different thicknesses and/or materials of different physical properties are used to reduce weight of a part. However, it also increases the weight of the part to some extent, which requires rework of stamping die to accommodate different thicknesses of the blank. Moreover, a few more manufacturing processes and systems, such as multiple shearing dies, material handling, finishing, oiling of blanks are required that adds to overall production of the part. Therefore, there is a need for a new way to enhance strength of sheet steel.

SUMMARY OF THE INVENTION

In view of the above problems of the convention art, one aspect of the present invention is to offer strength enhancement of sheet steel by forming hard beads therein, without increasing weight and cost thereof, and additionally offering design and manufacturing flexibilities.

Another aspect of the present invention is to enhance strength of single piece sheet steel by forming hard beads therein by melting and re-solidifying.

Another aspect of the present invention is to provide options to form hard beads in a single piece of sheet steel before or after stamping.

Another aspect of the present invention is to offer the strength enhancement of one or more selected zones of a single piece of the sheet steel by applying hard beads therein in a preferred pattern.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the present invention will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with accompanying drawing of which:

FIG. 1: Shows views of a single piece of sheet steel including a hard bead therein, (a) perspective view, (b) cross-sectional view; and

FIG. 2: Shows exemplary hard bead patterns on a single piece sheet steel.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Reference now will be made in detail to the embodiments of the present invention, an example of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. The embodiments are described below in order to explain the present invention by referring to figures.

References are made to FIG. 1 as an example of hard bead 40 formed across the thickness of a single piece sheet 20 of steel (e.g. rolled steel). The hard bead 40 is formed to have an elongated shape extended in a surface direction in which tensile strength of the single piece sheet 20 is to be enhanced. The hard bead 40 is formed by melting and then quickly re-solidifying a selected zone of the single piece sheet 20. The steel in the selected zone can be melted by application of conventional technology; for example, by application of high energy laser beam, by application of high energy electron beam, by application of high temperature flame, etc. However, the scope of the present invention is not limited to any specific method of melting. The above mentioned melting of sheet steel by application of laser beam, electron beam, high temperature flame etc. is known in the conventional art, therefore detailed descriptions of heat sources here is redundant. If necessary, a small amount of chemical agents can be added when the selected zone is in molten state. The hard bead 40 thus formed offers increased tensile and bending strength as compared to the base steel; and in turn, hard bead 40 being present in the single piece sheet 20, enhances overall tensile and bending strengths thereof. As a result, the overall tensile and bending strength of the single piece sheet 20 is enhanced without increasing its weight. It is to be emphasized that the scope of the present invention is not limited to the presence of hard bead 40 spanning across the total thickness of the single piece sheet 20 as apparent in the above description and as illustrated above in FIG. 1( a), rather, hard bead 40 can be formed to occupy only a partial thickness of the single piece sheet 40 as deemed necessary. Structurally, the hard bead 40 in the single piece sheet 20 is analogous to a rebar in concrete.

The single piece sheet 20 can be of low cost wrought steel and soft steel which is suitable for stamping and forming structural or non-structural parts. While the thickness T of the single piece sheet 20 is not limited to any thickness for the concept of this invention; however, for most practical purposes, the thickness T can range from 0.01 mm to about 10 mm and more preferably from 0.02 mm to about 3.5 mm. The length of the hard bead 40 is predetermined by the desired strength requirement of the part to be made from the single piece sheet 20.

A plurality of beads can be employed instead of a single bead. The plurality of beads can have different dimensions and shapes (i.e. straight and curved), and can be arranged in a pattern P, predetermined by a strength requirement of the part to be made before the stamping operation of the single sheet 20. The plurality of the hard beads 40 can be placed, adjacent to each other with an overlap, and/or with spacing. The pattern P and an amount of overlap or spacing can be determined on the basis of part functionality and design requirements by using other known techniques; for example, fine element analysis.

It is to be mentioned that the hard bead 40 can be formed before or after a stamping operation whichever is deemed more suitable for manufacturing a part or for repairing of a part after it has been manufactured. Any wrought, soft steel etc. can be treated by method according to the present invention. Both coated (galvanized steel etc.) and uncoated sheets may also be treated by the method of present invention.

A typical hard bead 40 of width W may range from 0.01 mm to 10.0 mm, but preferably from 0.05 mm to 4.0 mm, in a single pass of the energy source that is applied on the single sheet 20.

The operation of hard bead 40 formation may be done in an inert environment depending on the process of melting. In some melting processes, it is important to prevent the steel from being oxidized by oxygen present in the ambient air, and so an inert gas should be used as a so-called “cover gas”, as known in the art of welding and metal working. Description of cover gas is well-known in the art and its detailed description can be found in the conventional art.

From the foregoing detailed description, it will be evident that there are a number of changes, adaptations and modifications of the present invention which come within the scope of those skilled in the art. However, it is intended that all such variations, not departing from the spirit of invention, be considered as within the scope thereof as limited solely by the claims appended hereto. 

What is claimed is:
 1. A single piece sheet of steel comprising: a hard bead provided within the thickness of the single piece sheet to increase a tensile and bending strength of the single piece sheet, wherein, the hard bead is formed by melting and re-solidifying a portion of the single piece sheet, and the hard bead is not formed as a part lap welding or butt welding.
 2. The single piece sheet according to claim 1, can be made from low carbon steel.
 3. The single piece sheet according to claim 1, can be in the form of rolled steel.
 4. The single piece sheet according to claim 1, can be a coated steel sheet.
 5. The single piece sheet according to claim 4, can be a galvanized steel sheet.
 6. The single piece sheet according to claim 1, wherein, the hard bead can be formed before the single piece sheet is stamped to form a part.
 7. The single piece sheet according to claim 1, wherein, the hard bead can be formed after the single piece sheet is stamped to form a part.
 8. The single piece sheet according to claim 1, wherein a thickness of the single piece sheet may be in the range from 0.01 mm to about 50 mm, and more preferably from 0.02 mm to about 10.0 mm.
 9. The single piece sheet according to claim 1, wherein the hard bead spans across the total thickness of the single piece sheet from one face to another.
 10. The single piece sheet according to claim 1, wherein the hard bead spans only a portion of the total thickness of the single piece sheet.
 11. The single piece sheet according to claim 1, wherein the hard bead has a width from 0.01 mm to 10.0 mm and more preferably from 0.05 mm to 4.0 mm. 